Since JP-A-2008-236408 provides an information processing apparatus that detects a bus in which communication is abnormal because there is an ECU transmitting an error frame, and specifies the ECU connected to the bus and having an abnormal transmission cycle of a message frame, as a technology which detects communication abnormality and controls the relay of communication, and a relay apparatus is described which is connected to a plurality of ECUs connected through a multiplex communication bus through a relay connection unit, the relay connection unit relaying the communication of the ECUs, in which the relay connection unit includes a counter which is means for detecting communication abnormality and counts the number of message frames m received from the ECUs through the bus, for each ID (identifier) that is assigned to each message frame, and counter value check means for determining whether or not the communication of a message frame is abnormal by comparing the number counted by the counter with a reference value per unit time that is set in advance.
A relay apparatus described in JP-T-2007-528621 is configured to detect unauthorized access and disconnect a communication channel, and in order to secure another communication channel, the relay apparatus determines whether or not unauthorized access is detected by verifying a communication header of a received packet, based on an access pattern DB, identifies an in-vehicle communication apparatus of a transmission source of the packet when it is determined that unauthorized access is detected, and transmits a control signal for disconnecting the connection of the in-vehicle communication apparatus. Further, the relay apparatus transmits the control signal, and secures a communication channel through another in-vehicle communication apparatus by updating a channel control table.